A. We are studying the molecular mechanisms by which estrogens specifically alter growth of human breast cancer. 1. We have introduced viral onc genes (ras and myc) into human breast cancer cells. These retroviruses are stably integrated and viral mRNA is expressed at high levels. Effects on cell phenotype are under investigation. 2. We are using the technique of differential hybridization to identify specific estrogen regulated genes for cloning and subsequent analysis. 3. We have identified and partially purified several estrogen induced growth factors which are secreted by breast cancer cells into the medium. Some of the activities cross react with EGF receptor and are candidate novel transforming growth factors. Others cross react in IGF-1 type assays. 4. We have successfully prepared monoclonal antibodies to the secreted proteins of human breast cancer cells. One is an antibody against one of the growth factors. These antibodies and their antigens are being characterized and their biological activity is being assessed in vitro and in nude mice. 5. We have examined the regulation of thymidine kinase on estrogen regulated enzyme, activity by using a cDNA for human thymidine kinase.